1. FIELD OF THE INVENTION
The present invention relates to pre-filtering apparatus which are used to pre-filter air before the air is used for its intended purpose. The field of the present invention specifically relates to vacuum cleaners and an apparatus for pre-filtering air and concentrating and aggregating the dirt before it is either blown or sucked into the vacuum cleaner bag for the purpose of trapping dirt inside the vacuum cleaner bag.
2. DESCRIPTION OF THE PRIOR ART
A vacuum cleaner is an appliance, usually run on electricity, which is used for cleaning surfaces such as floors, carpets, tapestry or upholstered work, by cleaning means which involve suction. A modern vacuum cleaner develops its suction by means of a fan which discharges a powerful stream of air from the rear end of the casing. This sets up a powerful inflowing current of air which carries along any dust particles from the carpet or floor to which the suction nozzle is applied. The fan is usually driven by a small high-speed universal motor. A universal motor can be work on either alternating current or direct current. The fan has a large number of blades set at an angle. Their rotation sets up a flow of air in the axial direction. The air stream is passed through a filter in which the dust is precipitated and collected. In conventional bag type vacuum cleaners, the air is inhaled through a suction nozzle which picks up dirt and dust from a surface such as a carpet. A sufficiently powerful airflow to carry along dust and grit particles must be set up. Such air flow is induced by the suction developed by the fan. The air passes through a flap valve and into the filter bag and from there it exits the filter bag via tiny pores in the filter bag and is blown out of the rear end or other exit opening; the dust and dirt thereby being trapped in the bag. The fan and motor can be located ahead of or behind the bag.
A significant problem with prior art bag collection type vacuum cleaners is that the effective suction power gradually diminishes because of the increasing air flow resistance as the tiny pores of the filter bag becomes obstructed with dust particles.
One improvement known in the prior art is used in good quality hand held vacuum cleaners. These units have a small dust collecting chamber ahead of the filter.
In general, the problem with prior art bag type vacuum cleaners is illustrated in FIG. 1. For purposes of the present discussion, the key elements of prior art positive pressure bag filter vacuum cleaners are illustrated at 200. The air from the surface to be cleaned is sucked into the vacuum cleaner through air intake 202 and pushed by the motor 204 and its fan into the filter bag 210. The bag 210 comprises at least one filter membrane or filter bag 212. The air flow 220 is blown onto the surface of the filter membrane 212 and therefore the dust and dirt sucked in through air intake 202 is also blown onto the surface of the filter membrane 212 through the positive pressure of the air 220 being pushed onto the filter membrane 212. Positive pressure is defined as pressure in the direction of the retention surface of a filter membrane or filter bag, pressing particular matters onto the retention surface, resulting in obstruction of the pores of the filter membrane or bag. The retention surface is defined as that surface of one filter membrane or bag that faces the particulate matters and that which faces away from the clean, filtered air. As a result of this positive pressure flow of air 220 onto the surface of the filter membrane 212, particulate matters are trapped within the matrix of the filter membrane 212 and quickly diminishes the cleaning capability of the vacuum cleaner.
Therefore, a significant need exists to eliminate the problem of the clogging of filter membranes or filter bags within vacuum cleaners to thereby prolong the suction capability of the vacuum cleaner.